Refrigerant

Alternatives to R134a

In automotive air conditioning systems with open compressors and hose connections in the refrigeration cycle, the risk of leakage is much higher than with stationary systems. Therefore, with a view to reducing direct emissions in this area of ​​application, an EU Directive (2006/40 / EC) was adopted. Among other things, in the framework of new vehicle type approvals since 2011, only refrigerants with a GWP <150 have been approved. This eliminates the previously used in these systems R134a (GWP = 1430).

Meanwhile, alternative refrigerants and new technologies have been developed and tested. In this context, the use of R152a was further investigated. For some time, however, the automotive industry has agreed on system solutions with so-called "low GWP" refrigerants. The latter are discussed below.

R152a - an alternative to R134a (?)

R152a is very similar in terms of volumetric cooling capacity (about -5%), pressure levels (about -10%) and energy efficiency compared to R134a. Mass flow, vapor density and thus also the pressure drop are even cheaper (about -40%). R152a has been used as a component in blends for many years but not as a single-fluid refrigerant. Particularly advantageous is the extremely low global warming potential (GWP = 124).

However, R152a is flammable - due to the low fluorine content - and classified in safety group A2. This means increased safety requirements that require individual constructive solutions and safety measures as well as appropriate risk analyzes. For this reason, the use of R152a in vehicle air conditioning systems is unlikely.

"Low GWP" HFO refrigerant R1234yf and R1234ze (E)

The ban on the use of R134a in automotive air conditioning systems within the EU has initiated a number of research projects. In addition to CO 2 technology (page 35), refrigerants with very low GWP values ​​and similar thermodynamic properties as R134a have now been developed. At the beginning of 2006, two refrigerant blends were initially introduced under the names "Blend H" (Honeywell) and "DP-1" (DuPont). INEOS Fluor followed with another variant under the trade name AC-1. All refrigerants were, in the broadest sense, mixtures of different fluorinated molecules.

During the development and testing phase it became obvious that not all acceptance criteria could be met. Further investigations with these mixtures were therefore discontinued.

DuPont (now Chemours) and Honeywell combined their research and development activities in a joint venture focused on 2,3,3,3-tetrafluoropropene (CF3CF = CH2). This refrigerant, designated R1234yf, belongs to the group of hydro-fluoro-olefins (HFO). These are unsaturated HFCs with a chemical double bond.

The global warming potential is extremely low (GWP 100 = 4). Upon release into the atmosphere, the molecule breaks down rapidly within a few days, resulting in a very low GWP. However, this raises certain concerns about the long-term stability in the refrigeration cycle under real conditions. Extensive tests, however, have shown that the required stability for automotive air conditioning systems is met.

In the meantime, it has been determined that the potentially increased risk of flammability of the refrigerant in vehicle air conditioning systems can be avoided by appropriate design measures. However, there are also studies (eg by Daimler-Benz), in which an increased risk was detected. Various manufacturers have therefore intensified the development of alternative technologies again.

Toxicity studies show very positive results. The same applies to compatibility tests with the plastic and elastomeric materials used in the refrigeration cycle. Lubricants sometimes show an increased chemical reactivity, which can be suppressed by appropriate formulation and / or addition of "stabilizers".

The operating experience gained so far in laboratory and field tests give reason for a positive assessment, especially with regard to the performance and efficiency behavior. Cooling capacity and coefficient of performance (COP) are within the range of about 5% of the normal applications of automotive air conditioning in comparison to R134a. If the system is adapted accordingly, the same performance and efficiency can be achieved as with R134a.

Critical temperature and pressures are also similar, vapor densities and mass flow about 20% higher. The discharge gas temperature is up to 10 K lower in this application.

In view of the relatively simple conversion of automotive air conditioning systems, this technology has prevailed over the competing CO 2 systems.

However, as explained earlier, due to the flammability of R1234yf, further technical solutions are coming into focus.

These include active extinguishing equipment (eg with argon), but also the further development of CO 2 systems.

Further applications for HFO refrigerants

The use of R1234yf in other mobile climate applications is also considered, as well as in stationary air conditioning and heat pump systems. However, the fill level limits for A2L refrigerants (eg EN378) must be taken into account, which limit the use accordingly. There are also questions about the long-term stability in the refrigeration cycle in the usually very long life cycles of such systems.

For applications requiring operation of A1 (neither flammable nor toxic) refrigerants, R134a alternatives with lower GWP based on HFO / HFC blends have already been developed. They have been used in real facilities for some time.

R1234yf, as well as the R1234ze (E) described below, are also used as basic components in HFO / HFC blends. These blends have been developed as "Low GWP" alternatives to R134a, R404A / R507A, R22 / R407C and R410A to meet regulatory requirements for reducing F-Gas emissions (eg EU F-Gases Regulation). Some of these refrigerants have already been tested in terms of refrigeration capacity and efficiency as part of AHRI's Alternative Refrigerants Evaluation Program (AREP), and have also been used in real facilities.

From the group of hydro-fluoro-olefins is another substance with the name R1234ze (E) is available, which has been used mainly as a propellant for PU foam and aerosol. R1234ze (E) differs from R1234yf by a different molecular structure. The thermodynamic properties also provide favorable conditions for use as a refrigerant. The global warming potential is also very low (GWP100 = 7).

There is some uncertainty about flammability. In safety data sheets, R1234ze (E) is declared non-flammable. However, this only applies to transport and storage. When used as a refrigerant, there is a higher reference temperature for flammability tests of 60 ° C. At this temperature, R1234ze (E) is flammable and therefore classified as R1234yf in safety group A2L.

R1234ze (E) is sometimes referred to as R134a substitute but is more than 20% lower in volumetric refrigeration capacity than R134a or R1234yf. The boiling point (-19 ° C) also limits the application at lower evaporation temperatures strong. The preferred use is therefore in liquid chillers and high temperature applications. For more information, see page 36, "Special applications".

With kind permission of Bitzer Kühlmaschinenbau GmbH 

Source: Bitzer Refrigerant Report 19 

INTRODUCTION

Refrigerant is essential as an operating fluid for heat transport in refrigeration systems, air conditioning systems and heat pumps. There are different types of refrigerants with different environmental impacts should they be released into the atmosphere.

We explain which refrigerants you are allowed to use and which refrigerants are no longer allowed according to regulations.

Refrigerant types

There are different types of refrigerants that have been used over time. In the past, greenhouse gases (HCFCs) containing chlorine, such as R-12 or R-22 (chlorodifluoromethane), were often used as refrigerants. These have been replaced by chlorine-free refrigerants, such as R404A, R-134a or R-32, due to their harmful effects on the ozone layer.

Natural refrigerants such as propane, butane, isobutane, CO2 or ammonia have a better environmental balance compared to synthetically produced ones. Even water can be used as a refrigerant and is the most environmentally friendly of all.

Damage to the ozone layer

Older chlorinated refrigerants (HCFCs) contribute to the destruction of the ozone layer, leading to an increase in UV radiation on the Earth's surface. The Montreal Protocol provides for the gradual phase-out of these ozone-depleting refrigerants. What is unique about this protocol is that it was ratified by all 187 UN member states in 1988.

Currently, 193 member states are counted.

Several amendments to the protocol have tightened the regulations, most recently the decision in Kigali in 2016. Partially fluorinated substances (HFCs) are included in the Montreal Protocol and regulate the gradual restriction of the consumption of such refrigerants.

The global warming effect

Besides the depletion of the ozone layer, there is another known problem with refrigerants.

These can make a significant contribution to increasing the greenhouse effect in the atmosphere. When refrigerants enter the atmosphere, heat radiation from the sun is absorbed. This contributes to global warming.

Therefore, the Global Warming Potential (GWP) is an important factor in assessing the environmental impact of a refrigerant.

The F-Gases Regulation and the Montreal Protocol regulate the phasing out of refrigerants with a high GWP value.

Manufacturers are working hard to develop alternative refrigerants with a low GWP value.

The difficult thing is that the "old" refrigerants have a high safety class, which is more difficult to comply with if the GWP value is minimised.

Roughly speaking, the lower the GWP value, the greater the flammability.

The more flammable a refrigerant is, the lower its safety class.

The lower the safety class, the higher the technical requirements for operating systems with such refrigerants.

Environmentally friendly alternatives are sought

Modern refrigeration and air conditioning systems are increasingly using more environmentally friendly refrigerants with lower GWP.

For example, R-410A, a commonly used refrigerant in air conditioning systems, has no ozone depleting potential (ODP value), but it has a high GWP value of 2088. Other refrigerants such as: R-32 have a lower GWP value of 675 and are currently considered a more environmentally friendly alternative.

In the F-Gas Regulation, the phase-down process for all member states regulates the phasing out of refrigerants by 2030, which refrigerants are no longer allowed at which point in time and how long existing systems may be operated. Additional findings from current research can accelerate the phase-down process.

For example, it should be clarified by October 2023 how fluorinated carbon chains, in which the hydrogen atoms are completely or partially replaced by fluorine atoms, are to be handled. This will primarily affect the refrigerants of the R-400 and R-100 series.

According to current knowledge, the so-called PFAS are carcinogenic and difficult to break down in the human body.

PFASs are widespread in various industries and applications.

This does not only apply to refrigerants in refrigeration and air conditioning systems, but also to the air conditioning industry:

• Coatings for textiles 
• Outdoor clothing
• Impregnations
• Baking paper
• Fire extinguishers 
• Cosmetics 
• etc.

Leaks and maintenance

Refrigerant can be released into the atmosphere due to leaks in the system or improper maintenance. Proper handling of the refrigeration and air-conditioning systems, as well as regular leakage tests, are important in order to eliminate or minimise environmental pollution.

The use of detachable screw connections in refrigerant pipelines should be avoided. Where technically possible, fixed connections should be made by welding or soldering in the pipe network.

Depending on the filling quantity of the system or the CO2 equivalent of the refrigerant, system documentation is mandatory.

Disposal

When replacing or disposing of refrigeration and air conditioning equipment, local environmental regulations and disposal guidelines for the refrigerant contained therein must be followed. Refrigerant must be recovered from the refrigerant circuit and properly disposed of or recycled.

Conclusion

It is important to use environmentally friendly refrigerants in refrigeration and air conditioning systems to reduce environmental impact.

If it is technically possible, if the application allows it, natural refrigerants are the most likely to be used.

Care and maintenance of refrigeration and air conditioning systems is essential. It should be carried out by specialists or by persons who have the necessary know-how, tools and are informed about and certified in the latest environmentally friendly technologies.

If you notice any defects, report them to your service partner as soon as possible.

Regular maintenance of the equipment is the be-all and end-all. Not only for the environment, but it also saves you money.

Properties of Ammonia

Ammonia is toxic. It is a pungent gas that affects the respiratory organs and mucous membranes.

Ammonia is flammable. The ignition limit is 630°C, in the absence of catalytic steel even 850°C.

Ammonia cannot be ignited with a burning shaving, but it can be ignited with a welding torch.

Ammonia is explosive. The lower explosion limit in connection with air is 15.0%, the upper explosion limit is 30.2% (related to 20°C and 1.013 bar).

Why has such a dangerous substance been used as a refrigerant for 120 years?

• The manufacturing costs are low.
• The thermodynamic properties are favorable compared to other refrigerants.
• The ecological values ​​are fine: ODP = 0, GWP = 0.
• Perceptions at 5 -10 ppm (volume in air)

ppm - parts per million -   the millionth part of a unit

Usable Materials

The main material used is steel and its alloys. Galvanic surfaces are destroyed by ammonia.

Zinc is completely dissolved by ammonia in the presence of water.

Copper cannot be used as a material. Ammonium hydroxide forms in the presence of water. This readily dissolves copper to form the characteristic blue-colored copper-ammonium complex.

Phosphor bronze is the most resistant to ammonia. It is used in shaft seals. Alternative material is carbon and silicon carbide.

Mercury forms explosive mixtures with ammonia, and the addition of bismuth amalgam can help.

What are the concentration limits?

• MAK value 50 ppm
• 300 ppm hardly tolerable. Still harmless if exposed for more than an hour.
• 700 - 1,000 ppm unbearable. Prolonged exposure will damage the respiratory tract.
• 2,000 - 3,000 ppm fatal after 0.5 - 1 hour. Corneal inflammation occurs in the eyes.
• 5,000 - 6,000 ppm leads to blindness and death after 30 minutes

In the early 1980s, the international debate on the elimination of HCFCs and CFC refrigerants began, and with it the search for alternatives. It was decided to gradually reduce the use of these refrigerants by 2040 and then ban them altogether.

R22 was explicitly part of this solution. In the US, the use of R22 even increased thereafter, as the agreed goals were generally seen as unrealistic and it was believed that developing countries needed more time for a total phasing out of CFCs.

In the meantime, a global change of mind has begun, and accordingly, the 19th Conference of the Parties to the Montreal Protocol in September 2007 set stricter rules for phase-out periods:

Industrialized countries or non-Article 5 states: 
Reduction of production and use of HCFCs (R22) by 75% by 2010 and by 90% by 2015; CFC ban from 2020.

Developing countries according to Article 5: 
Reduction of production and use of HCFCs (R22) by 1% by 2010, by 35% by early 2020 and by 67.5% by 2025. Complete phase-out 2030. 2.5% of original CFCs Quantity are still allowed until 2040.

The accelerated phasing out of CFC over the next ten years means that it will no longer be possible to operate new plants with CFCs in both industrialized and developing countries . 

In the United States, the Environmental Protection Agency (EPA) has established specific provisions to implement the Montreal Protocol, which aims to phase out R22 use by 2010. However, devices manufactured before 2010 can continue to operate until 2020.

To achieve this goal, several initiatives have been launched, including the EPC's GreenChill Advanced Refrigeration Partnership. It involves companies in the food industry as well as refrigeration equipment and refrigerant manufacturers. The partnership aims to help supermarkets withdraw R22. Currently, it is still used in more than 70% of US supermarkets. HFCs are clearly favored as an alternative in the US, as will be seen, for example, at the opening of the world's largest production facility for R32 in September 2007. The plant in Colvert City, Kentucky produces 25,000 tons of R32 per year. R32 is a component of HFC refrigerant blends such as R410A.

The new provisions have no impact on European legislation. The deadline for the complete ban on R22 in existing facilities is 31.12.2014. Use in new cooling, air conditioning or heat pump systems has been prohibited since January 2001. The use in combined air conditioning and heat pump systems since January 2004 prohibited.

Copyright Danfoss A / S (RA Marketing / MWA) June 2009

The refrigerant R1234ze(E) is a low flammable refrigerant and has a global warming potential ( GWP ) of less than 1. R1234ze(E) is an HFO (hydrofluoroolefin) refrigerant. 

It is suitable for operation in chillers / chillers and heat pumps for commercial and industrial plants with positive displacement compressors and direct evaporation. It is classified according to ISO / ASHRAE in the safety class A2L (hardly flammable) and therefore allows significantly higher quantities than other flammable refrigerants.

With its GWP value of less than 1, R1234ze(E) falls below the limit of 150 set out in the F-Gas Regulation 517/2014 and the Ecodesign Directive. It is therefore not within the limits of the F-gas Regulation . Down scenario, because this refrigerant does not include any CO2 equivalents on the quantity of refrigerants placed on the market. R1234ze (E) is a low-flammability class 2L refrigerant. The permitted capacities, system configurations and guidelines for safe handling for the respective applications can be found in the applicable regulations and standards for your region, eg. PED, EN 378 or ISO 5149.

Applications for HFO refrigerants

R1234ze(E) is used inter alia as a basic component in HFO / HFKW blends. These blends have been developed as "Low GWP" alternatives to R404A / R507, R22 / R407C and R410A to meet regulatory requirements for reducing F-Gas-emissions (EU-F-Gases Regulation). Some of these refrigerants have already been tested in terms of refrigeration capacity and efficiency as part of AHRI's Alternative Refrigerants Evaluation Program (AREP) and also used in test facilities.

From the group of hydro-fluoro-olefins is another substance with the name R1234ze(E) is available, which has been used mainly as a blowing agent for PU foam and aerosol. R1234ze(E) differs from R1234yf by a different molecular structure. The thermodynamic properties also provide favorable conditions for use as a refrigerant. The global warming potential

is also very low (GWP100 = 7).

There is some uncertainty about flammability. In safety data sheets, R1234ze(E) is declared non-flammable. However, this only applies to transport and storage. When used as a refrigerant, there is a higher reference temperature for flammability tests of 60 °C. At this temperature, R1234ze(E) is flammable and therefore classified as R1234yf in safety group A2L.

R1234ze(E) is sometimes referred to as R134a substitute but is more than 20% lower in volumetric refrigeration capacity than R134a or R1234yf. The boiling point (-18 °C) also limits the application at lower evaporation temperatures strong. With positive displacement compressors, therefore, the preferred use is in high temperature applications.

application areas

1. Air conditioning
2. Heat pumps
3. Commercial refrigeration
4. Chillers
5. industrial air conditioning

refrigeration plant

1. Direct expansion
2. new plants

Technical specifications

Carbon dioxide R744 (CO2) as an alternative refrigerant and secondary fluid

CO2 has a long tradition in refrigeration that goes well into the second to last century. It has no ozone depletion potential, a negligible direct greenhouse effect (GWP = 1), is chemically inactive, non-flammable and in the classical sense non-toxic. Therefore, CO2 is also not subject to the stringent requirements with respect to system tightness, such as HFCs (F-Gas Regulation) and flammable or toxic refrigerants. However, the lower limit in air compared to HFCs has to be considered. In confined spaces appropriate safety and monitoring equipment may be required.

CO2 is also inexpensive and there is no need for recovery and disposal. In addition, a very high volumetric cooling capacity, depending on the operating conditions such as the 5- to 8 times by R22 and NH3 corresponds.

Above all, the safety-relevant properties were a major reason for the initially widespread use. Focus in the application were eg ship refrigeration systems. With the introduction of "(H) CFC safety refrigerants" CO2 was pushed back and had almost disappeared from the market since the 1950s. Significant causes are the thermodynamic properties which are relatively unfavorable for customary applications in refrigeration and air conditioning technology.

The pressure of CO2 is extremely high and the critical temperature of 31 °C (74 bar) is very low. Depending on the heat carrier temperature on the high pressure side, this requires a transcritical operation with pressures well above 100 bar. Under these conditions, the efficiency compared to a conventional cold steam process (with liquefaction) is usually lower and thus the indirect greenhouse effect correspondingly higher.

Nevertheless, there are a number of applications where CO2 can be used very economically and with favorable eco-efficiency. These include, for example, subcritically operated cascade systems, but also transcritical systems in which the temperature sliding on the high pressure side can be advantageously used or the system conditions allow a subcritical operation over long periods of  operation. In this context, it should also be noted that the heat transfer values ​​of CO2 are significantly higher than other refrigerants with the potential of very low temperature differences in evaporators, condensers and gas coolers. In addition, the required pipe cross-sections are very small and the influence of the pressure drop comparatively low. When used as a secondary fluid, the energy requirement for circulating pumps is also extremely low.

In the following, some examples of subcritical systems and the resulting design criteria will be discussed. An additional section is followed by explanations of transcritical applications.

Fig. 29/1 R744 (CO2) - pressure / enthalpy diagram

Fig. 29/2 R744 (CO2) / R22 - Comparison of pressure levels

Subcritical application

An application that is also very advantageous from an energy point of view and with regard to pressure situations is suitable for industrial and larger commercial refrigeration systems. For this purpose, CO2 can be used as a secondary fluid in a cascade system - if necessary in combination with a further compression stage for lower evaporation temperatures (Fig. 30/1). 

The mode of operation is subcritical in each case and thus ensures good profitability. In the favorable application range (about -10 to -50 °C), the pressure levels are still at a level for which already available or in development components (eg for R410A) can be adapted with reasonable effort.

Resulting design and execution criteria

For the high-temperature stage of such a cascade, a compact cooling set can be used whose evaporator on the secondary side serves as a condenser for CO2 . Suitable refrigerants are chlorine-free substances (NH3 , HC or HFC, HFO and HFO / HFC mixtures).

For NH3 , the cascade cooler should be designed to prevent the dreaded formation of deer horn salt in the event of leakage. In breweries this technique has been used for a long time.

In large refrigeration systems, the secondary circuit for CO2 in its basic structure largely corresponds to a low-pressure pump system, as is often carried out in NH3 systems. The essential difference is that the liquefaction of CO2 takes place in the cascade cooler and the collecting tank (separator) only serves as a storage tank. The extremely high volumetric cooling capacity of CO2 (latent heat through phase change) leads to a very low mass flow and enables small pipe cross-sections and minimal energy requirements for the circulation pumps. When combining with another compression level (eg for deep freezing) there are different solutions.

Fig. 30/1 shows a variant with additional collector, which is sucked off by one or more booster compressors to the required evaporation pressure. The compressed gas is also fed into the cascade, liquefied and discharged into the downstream collector. From there, the feed into the low-pressure separator (TK) via a float device. Instead of classical pump circulation, the booster stage can also be designed as a so-called LPR system (Low Pressure Receiver). This eliminates the need for circulating pumps, but the number of evaporators is more limited with regard to a uniform injection distribution of CO2 .

In the event of a prolonged system failure with a strong increase in pressure, the CO2 can be released to the atmosphere via safety valves. Alternatively, additional cooling units for CO2 liquefaction are used with which longer shutdown periods can be bridged without critical pressure increase. For systems in commercial applications, a version with direct expansion is also possible.

For this purpose, supermarket systems with their usually widely branched pipe network and blast freezer offer particularly good potential. The normal cooling system is then carried out conventionally or by means of a secondary circuit and combined for deep cooling with a CO2 cascade system (for subcritical operation). A system example is shown in Fig. 30/2.

For a general application, however, not all conditions are currently met. It has to be taken into consideration that in many respects changed plant engineering as well as specially coordinated components become necessary.

Fig. 30/1 Cascade system with CO2 for industrial application

Fig. 30/2 Conventional refrigeration system combined with CO2 freezing cascade

The lubricants are also exposed to very high requirements. Conventional oils are usually immiscible and therefore require complex measures for the return from the system. On the other hand, the use of miscible or readily soluble POE must take into account a strong reduction in viscosity. BITZER offers two series of special compressors for subcritical CO2 applications.

Transcritical application

The transcritical process is characterized by the fact that the heat removal on the high pressure side is isobaric but not isothermal. In contrast to the liquefaction process in subcritical operation, this gas cooling (decompression) takes place with appropriate temperature sliding. The heat exchanger is therefore referred to as a gas cooler. As long as the operation is above the critical pressure (74 bar), only high-density steam is delivered. Liquefaction does not take place until after expansion to a lower pressure level for example by intermediate relaxation in a medium pressure collector. Depending on the temperature profile of the heat sink, a system designed for transcritical operation can also be operated subcritically and under these conditions with improved efficiency. In this case, the gas cooler becomes a condenser.

Another special feature of transcritical operation is the necessary regulation of the high pressure to a defined level. This " optimum pressure" is determined as a function of the outlet temperature of the gas cooler by balancing between the greatest possible enthalpy difference and at the same time minimum compaction work. It must be modulated by an intelligent controller to the respective operating conditions (see system example, Fig. 31).

As described in the beginning, the transcritical mode of operation appears to be unfavorable in terms of energy efficiency in purely thermodynamic terms. This is also true for systems with a relatively high temperature level of the heat sink on the high pressure side. However, additional measures can be taken to improve efficiency such as the use of parallel compression (Economiser system) and / or injectors and expander to recover the throttle losses during the expansion of the refrigerant. Apart from that, there are applications in which the transcritical process is energetically generally advantageous. These include, for example, heat pumps for hot water heating or drying processes.

In the usually very high temperature gradient between pressure gas inlet into the gas cooler and inlet temperature of the heat sink, a very low gas outlet temperature can be achieved. This is favored by the course of the temperature sliding and the relatively high average temperature difference between CO2 vapor and heat transfer fluid. The low gas outlet temperature leads to a particularly high enthalpy difference and thus to a high system performance figure. Hot water heat pumps of smaller power are already being produced and used in large quantities. Systems for medium to larger services (eg hotels, swimming pools, drying systems) must be individually planned and executed. Their number is therefore still limited, but with a good upward trend. In addition to these specific applications, there are also a number of developments for the classic areas of refrigeration and air conditioning. These include, for example, supermarket refrigeration systems. In the meantime, plants with compressors in the parallel network are already being used on a larger scale.

These are predominantly so-called booster systems, in which the normal and deep-freeze circuit is connected directly (without heat exchanger). The operating experience and calculated energy costs show promising results. However, the investment costs are still significantly higher than traditional systems with HFCs and direct evaporation. Reasons for the favorable energy costs are on the one hand on the already largely optimized components and the system control and the advantages described above with regard to heat transfer and pressure drop. On the other hand, these systems are preferably used in climates, which allow due to the seasonal temperature profile very high transit times in subcritical operation.

To further increase the efficiency of CO2 supermarket systems and their use in warmer climates, the previously described technologies with parallel compression and / or injectors are also increasingly being used . In this respect, but also with regard to the very demanding technology and the high demands placed on the qualification of planners and service specialists, CO technology can not be considered as a substitute 2 for systems with HFC refrigerants.

Resulting design and execution criteria

Detailed information on this would be beyond the scope of this information. In any case, system technology and control differ significantly from conventional systems. With regard to pressure, volume and mass flow conditions, specially developed components, control devices and safety devices as well as correspondingly designed pipelines must be used. Particularly demanding is the compressor technology. The special requirements require a completely independent construction. This applies, among other things, to design, materials (bursting safety), delivery volume, engine, design of working valves, lubrication system and compressor and engine cooling. The high thermal load severely restricts the area of ​​application for one-stage compaction. Deep-freezing requires two-stage operation, with a split into separate high and low pressure compressors in composite systems is particularly advantageous.

For the lubricants, the criteria described above in connection with subcritical systems apply even more . 

Development efforts are still required in various areas, but trans-critical CO2 technology can not generally be described as state of the art. For transcritical CO 2 applications BITZER offers a wide range of special compressors. The application is geared to specific applications, so individual testing and evaluation are required.

CO2 in automotive air conditioning systems

Within the framework of measures already discussed for a long time for the reduction of direct refrigerant emissions and the ban on the use of R134a in car air conditioning systems * existing in the EU, the development of CO2 systems has been intensively pursued for years . At first glance, the efficiency and thus indirect emissions of CO2 systems appear comparatively unfavorable under typical environmental conditions. However, it should be noted that the current R134a systems have lower efficiencies than equivalent stationary systems. The reasons for this are the specific installation conditions and the relatively high pressure losses in pipelines and heat exchangers. At CO2 the pressure drop has a much lower impact. In addition, the system efficiency is additionally favored by the high heat transfer values ​​in the heat exchangers.

For this reason, optimized CO2 air conditioning systems can achieve roughly the same efficiencies as R134a. In view of the usual leak rates of such systems, this results in a more favorable balance sheet with regard to the TEWI. From today's perspective, it is not possible to predict whether CO2 technology will be able to assert itself in this application in the longer term. This is certainly also dependent on experience with the "LowGWP" refrigerants, which have since been introduced by the automotive industry. Operational safety, costs and worldwide logistics will play an important role here.

Fig. 31 Example of a transcritical CO2 booster system

With kind permission of Bitzer Kühlmaschinenbau GmbH 

Source: Bitzer Refrigerant Report 19 

CO2  - R744 the refrigerant of the future?

The importance of CO2 for refrigeration applications has increased in recent years and the market is increasingly focusing on the refrigerant R744.

CO2 is a natural refrigerant and environmentally friendly and cost effective compared to fluorinated refrigerants. It is not flammable, non-toxic and colorless.

CO2 serves as the basis for calculating the CO 2 equivalent of all refrigerants. R744 has a GWP of 1 and is excluded from the phase-down scenario foreseen in the  F-Gas Regulation . According to the F-gas regulation, it is  necessary to check the tightness of the refrigeration system from a CO2 equivalent of 5 tonnes. This eliminates the leak tightness control for refrigeration systems with R744 with a capacity of 5 tonnes. During service work, refilling or decommissioning of refrigeration systems with CO2 , the refrigerant may leak into the environment. A costly recovery of the refrigerant is not necessary.

The disadvantage is the high operating pressure of the refrigerant, the low Ktirische point, the formation of dry ice when falling below the triple point and the very high standstill pressure. The requirements and selection of the components used in the refrigeration system must be taken into account accordingly. 

R744 is also an interesting alternative for the automotive industry. The air conditioning in the vehicle can be operated with environmentally friendly refrigerant. Compared to the current low-pressure refrigerant R134a, all components of the air-conditioning system must be able to withstand a high pressure of up to 135 bar. The good thermodynamic properties speak in favor of use in automotive air conditioning systems. 

The refrigerant R744 is non-combustible, non-toxic and colorless. R744 has a Global Warming Potential ( GWP ) of 1 (GWP = 1).  

R744 has an ODP (Ozone Depletion Potential ) of 0. 

R744 is  classified in safety class A1 according to ISO / ASHRAE  .

application areas

• Commercial refrigeration
• Vehicle air conditioners
• Industriekälte
• heat pump
• 20 ° C to -40 ° C

refrigeration plant

• Direct expansion
• flooded evaporation
• new plants

Technical specifications

The refrigerant R448A is a zeotropic refrigerant mixture consisting of three components with different boiling temperatures. This results in a temperature glide of 6.2K at the phase change. R448A is suitable as a replacement and drop-in refrigerant for R404A inventory refrigeration systems and has a lower GWP value. R448A is particularly suitable for low and medium temperature applications. For single-stage refrigeration systems in the deep-freeze area, attention must be paid to the final compression temperature. Due to increased cylinder head temperatures, the use of a cylinder head fan may be necessary. Here, the technical specifications of the compressor manufacturers should be observed. 

The refrigerant R448A is non-flammable, non-toxic and colorless. R448A has a global warming potential ( GWP ) of more than 1 (GWP = 1387).  

R448A has an ODP (Ozone Depletion Potential ) of 0. 

R448A is  classified in safety class A1 according to ISO / ASHRAE  .

With its GWP value of more than 150, R448A is governed by the F-gas Regulation 517/2014. Thus, it is affected by the phase-down scenario provided for in the  F-Gas Regulation .

application areas

1. Commercial refrigeration
2. Industriekälte
3. industrial air conditioning
4. 20 ° C to -30 ° C

refrigeration plant

1. Direct expansion
2. new plants
3. Drop-in

Technical specifications

The refrigerant R32 is a single-component refrigerant.  It is very suitable for air conditioning applications, for cooling and heating operation. Among other things, R32 is intended to replace the refrigerant R410A. The saturation pressure of R32 is very similar to R410A. This means that the development of an R32 system can be based on the R410A system. R32 has a greater specific cooling capacity than R410A. 

The refrigerant R32 is difficult to remove, non-toxic and colorless. R32 has a global warming potential ( GWP ) of more than 1 (GWP = 675).  

R32 has an ODP (Ozone Depletion Potential ) value of 0. 

R32 is  classified in safety class A2L according to ISO / ASHRAE  .

With its GWP value of more than 150, R32 is subject to F-gas regulation 517/2014. It is thus affected by the phase-down scenario provided for in the  F-Gas Regulation , but it will meet the requirements by 2025.

application areas

1. Air conditioning (cooling and heating mode)
2. Commercial refrigeration
3. Chillers
4. industrial air conditioning
5. 20 ° C to -30 ° C

Refrigeration system

1. Direct expansion
2. New systems

Technical specifications

The refrigerant R407F is a zeotropic refrigerant mixture consisting of three components with different boiling temperatures. This results in a temperature glide of 6.4K at the phase change. R407F is suitable as a replacement and drop-in refrigerant for R22 existing refrigeration systems. R407F is particularly suitable for low and medium temperature applications. For single-stage refrigeration systems in the deep-freeze area, attention must be paid to the final compression temperature. Due to increased cylinder head temperatures, the use of a cylinder head fan may be necessary. Here, the technical specifications of the compressor manufacturers should be observed. 

The refrigerant R407F is non-combustible, non-toxic and colorless. R407C has a global warming potential ( GWP ) of more than 1 (GWP = 1825).  

R407F has an ODP (Ozone Depletion Potential ) value of 0. 

R407F is  classified in safety class A1 according to ISO / ASHRAE  .

With its GWP of more than 150, R407F is governed by the F-gas Regulation 517/2014. Thus, it is affected by the phase-down scenario provided for in the  F-Gas Regulation.

application areas

1. Climber
2. Commercial refrigeration
3. Chillers
4. industrial air conditioning
5. 20 ° C to -30 ° C

refrigeration plant

1. Direct expansion
2. new plants
3. Drop-in

Technical specifications